Practical Engineering: Simple King Truss for Ridge Beam Support

The triangle formed by a pair of rafters
and a joist is the most basic form of
truss, and has been in use in one form or
another for centuries. The two rafters
can be envisioned as leaning against
each other, just as you might lean a ladder
against a wall. The vertical forces on
the rafters are all transferred to the outer
corners of the base of the triangle, which
typically bears on the building walls
below. The load transfer creates a horizontal
force, which I refer to as rafter
thrust. This thrust is restrained by the
horizontal joist, which provides a
restraining force to keep the base of the
triangle (and the walls